1. Field of the Invention
The present invention relates to tools used in petroleum and gas wells. More particularly, the present invention is related to washing tools used when injecting treating fluids such as cleaning fluids into petroleum and gas wells which have depleted or low bottom hole pressure to clean the producing area of the well to increase bottom hole pressure and improve flow from the well. Even more particularly, the present invention is related to control valves used in petroleum and gas wells.
2. Description of the Related Art
In oil and gas wells that have been depleted or have low bottom hole pressure and were gravel packed when completed, it is known to inject cleaning fluids in the well to clean the gravel pack area of the well and/or the perforations in the casing to improve bottom hole pressure and improve flow from the well. Frequently, the cleaning fluids will seek the path of least resistance and clean out one to three feet of the perforated area of the tubing or casing in the well and the remainder of the perforated area are never contacted by the cleaning fluids and acid.
To prevent this from happening and to make sure every foot of the perforations get treated with cleaning fluids, it is known to insert tools having dual packer assemblies with injection ports between the packings in the well. The dual packer assemblies are actuated when pressure is applied from the surface to isolate the portion of the perforations to be treated. Exemplary of such tools having dual element packings is U.S. Pat. No. 4,279,306 issued Jul. 21, 1981 which is hereby incorporated by reference.
Occasionally, even when using washing tools having dual packer elements, cleaning fluids will escape to the surrounding strata, and large volumes of expensive cleaning fluid will be lost. All of the cleaning fluid in the tubing above the dual packer assemblies may be lost to the surrounding strata. If, for example, a gravel pack and/or casing perforations were being washed at a 10,000 foot depth, and tubing having a 1.25 inch diameter were being used, about 50 barrels of cleaning fluid costing several hundred dollars per barrel may drain from the tubing into the surrounding strata and be lost.
Furthermore, when fluid is being lost to the surrounding strata, the pressure between the dual packing elements drops below the pressure of the fluids above the top packer assembly between the washing tool and the casing, or production string inside the casing. Such pressure differential on each side of the top packer may lock the top packer assembly in the expanded position and prevent removal of the washing tool from the hole.
Exemplary of the patents of the prior art are U.S. Pat. Nos. 5,056,599; 4,562,854; 4,431,051; 4,421,174; 4,279,306; 4,257,484; 3,987,848; 2,959,225; 2,864,449; and Re. 28,588.